The iris is part of the human eye that can be seen through the cornea. It has three layers; endothelium, stroma, and the epithelium.

It is divided into two separate chambers; the anterior chamber which is located between the cornea and the iris, and the posterior which is located between the iris and the lens.

The iris resembles a camera shutter. When too much light enters the eye, the sphincter muscle draws the pupil inward. When the light is reduced the iris muscle that is wheel like twists and pulls outward creating a larger opening for the pupil.